1. Field of the Invention
The present invention relates to an automatic leveling apparatus which automatically tilts the light axis of a headlamp in such a direction as to offset a pitch angle (an inclination of a vehicle in the longitudinal direction thereof). More particularly, the present invention relates to an automatic leveling apparatus for automatically controlling the alignment of the light axis of the headlamp in a vertical direction on the basis of a pitch angle obtained while the vehicle is stationary.
2. Related Art
A headlamp of this type is built such that, for example, a reflector equipped with a light source is supported on a lamp body so as to be tiltable about a horizontal axis, and such that the light axis of the reflector (headlamp) can be pivoted about the horizontal axis by means of an actuator.
A known automatic leveling apparatus comprises pitch angle detection means and a vehicle speed sensor, both of which are mounted on a vehicle, and a control section for controlling operation of an actuator on the basis of detection signals output from the detection means and the sensor. The light axis of a headlamp (reflector) is controlled so as to constantly remain in a predetermined position relative to the road surface.
Automatic leveling comprises dynamic automatic leveling for constantly effecting an automatic leveling operation either while the vehicle is travelling or stationary, and static automatic leveling for effecting an automatic leveling operation while the vehicle is stationary.
During the dynamic automatic leveling operation, a leveling operation is performed in real time in response to a change in the orientation of a vehicle stemming from acceleration and deceleration during travel, as well as to a change in the weight of the vehicle stemming from loading and unloading of cargo on or from the vehicle during halts. For this reason, the actuator is operated a very large number of times, thus consuming a large amount of power. Further, components constituting a drive mechanism, such as a motor and gears, are required to have great durability, thus adding to cost.
In contrast, the static automatic leveling operation is basically directed toward a leveling operation performed during stoppage of the vehicle. For this reason, a correct pitch angle can easily be detected. Since the number of times the actuator is operated is small, power consumption is correspondingly low. Components constituting a drive mechanism, such as a motor and a gear, do not require great durability. Hence, the conventional automatic leveling apparatus is advantageously inexpensive. Such an automatic leveling apparatus has received attention from the headlamp industry.
When a vehicle stops while facing downhill or such that the wheels on one side of the vehicle are on the curb, the orientation of the vehicle is changed regardless of loads imposed on the vehicle (i.e., the sum of the weights of passengers and cargo). If the automatic leveling operation is carried out while the vehicle is stationary, the light axis of the headlamp may be changed excessively upward or downward, thus resulting in improper leveling.